Electronic devices used with wireless communication systems, such as cellular phones, GPS receivers, and Wi-Fi enabled notebook and tablet computers, generally contain signal processing systems that have interfaces to the analog world. Such interfaces may include wire line and wireless receivers that receive transmitted power and convert the received power to an analog or digital signal that may be demodulated using analog or digital signal processing techniques. A typical wireless receiver architecture includes a low noise amplifier (LNA) that amplifies the very small signals that may be received by an antenna and passes an amplified signal to later amplification and/or signal processing stages. By providing gain at the LNA, subsequent gain processing stages are made insensitive to noise, thereby enabling a lower system noise figure.
As portable wireless devices have evolved to support multiple standards, it is common for the RF signal path to contain various components such as antenna switches coupled between one or more antennas and one of more RF front end circuits. One example of such a circuit is a multi-standard cellular telephone that can make calls using different standards such as code division multiple access (CDMA), Global System for Mobile Communications (GSM), Long Term Evolution (LTE), and the like. In addition, a particular wireless device may also support IEEE 801.11 Wi-Fi operation and Global Positioning System (GSM). By using an RF switch, an RF front end circuit optimized for CDMA communication may be used for CDMA calls, while and RF front end circuit optimized for GSM communication may be used for GSM calls. In addition, RF switches may be used to implement adjustable matching networks for antennas and power amplifiers, and to provide adjusting tuning for high frequency filters by switching in and out and/or bypassing passive matching and tuning elements. Because attenuation in the RF signal path prior to the LNA may degrade the noise figure of an RF system, the introduction of antenna switches and other components prior to an LNA in order to support multi-standard operation poses various challenges with respect to maintaining an adequate system noise figure.